Question

I’m making a little app for calculating tips for Windows Phone 7 and I want to validate the inputs before trying to calculate things.

How can I check if the textbox has a valid monetary value inserted? No letters and no more than one Dot for decimal places.

Answer 1

The criteria you describe could be checked with a RegEx but it would make more sense to just check with decimal.TryParse()

string txt = MyTextBox.Text;
decimal value;

if (decimal.TryParse(txt, 
        NumberStyles.AllowDecimalPoint, 
        CultureInfo.InvariantCulture, out value))
{
    // got it
}

The NumberStyles and CultureInfo (IFormatprovider) are up for discussion.